This paper establishes the fundamental limits of a two-user single-receiver system where communication from User 1 (but not from User 2) needs to be undetectable to an external warden. Our fundamental limits show a tradeoff between the highest rates (or square-root rates) that are simultaneously achievable for the two users. Moreover, coded time-sharing for both users is fundamentally required on most channels, which distinguishes this setup from the more classical setups with either only covert users or only non-covert users. Interestingly, the presence of a non-covert user can be beneficial for improving the covert capacity of the other user.

翻译：本文建立了双用户单接收器系统的基本极限，其中用户1（而非用户2）的通信需要对外部监控者不可检测。我们的基本极限揭示了两个用户同时可实现的最高速率（或平方根速率）之间的权衡关系。此外，在大多数信道上，两个用户必须从根本上采用编码分时机制，这使该场景区别于仅有隐蔽用户或仅有非隐蔽用户的经典设置。有趣的是，非隐蔽用户的存在可能有助于提升另一用户的隐蔽容量。